1. Field of the Invention
The present invention relates to a ceramic substrate, an electronic apparatus, and a method for producing a ceramic substrate. Specifically, the present invention relates to a ceramic substrate mounted on a mounting board by connecting a conductor disposed on a first main surface of the ceramic substrate to a mounting land of the mounting board with solder, an electronic apparatus, and a method for producing the ceramic substrate.
2. Description of the Related Art
In a ceramic substrate, typically a ceramic substrate 50 is configured to be mounted on a mounting board 53 by connection between a land electrode 51 provided on a first main surface of the ceramic substrate 50 and a mounting land 54 of the mounting board 53 with solder 52, as shown in FIG. 10.
However, as shown in FIG. 10, when the land electrode 51 of the ceramic substrate 50 has a dimension that is substantially equal to that of the mounting land 54 of the mounting board 53, for example, a stress due to the difference in thermal expansion coefficient between the ceramic substrate 50 and the mounting board 53 during a heat-cycle test of a product concentrates on the edge of the land electrode 51, and in some cases, a crack C occurs in the ceramic substrate 50.
As shown in FIG. 11, a method for preventing the occurrence of a crack in the ceramic substrate 50 and a failure due to migration in the land electrode 51 by coating the periphery of the land electrode 51 with a glass layer 55 so as to relax stress concentration during heat-cycle test is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-231860 (Patent Document 1).
Patent Document 1 also discloses that a glass material of the glass layer 55 is preferably composed of a glass material primarily composed of a glass material incorporated in a ceramic material (dielectric ceramic layer) of the ceramic substrate 50 from the viewpoint of the enhancement of adhesion between the glass layer 55 and the ceramic substrate 50.
However, in accordance with a common method for producing a ceramic substrate, various types of plating films, such as a Ni plating film for preventing solder leaching, a Sn plating film for improving solderability, and an Au plating film for improving connection reliability, are formed on the surface of the land electrode 51 after the formation of the glass layer 55. Thereby, the plating resistance of the glass layer 55 is easily degraded, depending on the type of the glass material. This disadvantageously leads to the occurrence of a pinhole due to erosion caused by the plating solution.
When the glass layer 55 is composed of a glass material primarily composed of a glass material incorporated in a ceramic layer (dielectric layer) of the ceramic substrate 50 from the viewpoint of the enhancement of adhesion between the ceramic substrate 50 and the glass layer 55, the glass material incorporated in the ceramic layer is usually selected based on electrical properties and not based on plating resistance. Thus, disadvantageously, the plating resistance of the glass layer 55 is easily degraded, which causes serious problems due to erosion caused by the plating solution.